- Stoichiometric and catalytic C-F bond activation by the trans-dihydride NHC complex [Ru(IEt2Me2)2-(PPh3)2H2] (IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)
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The room temperature reaction of C6F6 or C6F5H with [Ru(IEt2Me2)2(PPh3)2H2] (1; IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) generated a mixture of the trans-hydride fluoride complex [Ru(IEt2Me2)2(PPh3)2HF] (2) and the bis-carbene pentafluorophenyl species [Ru(IEt2Me2)2(PPh3)(C6F5)H] (3). The formation of 3 resulted from C-H activation of C6F5H (formed from C6F6via stoichiometric hydrodefluorination), a process which could be reversed by working under 4 atm H2. Upon heating 1 with C6F5H, the bis-phosphine derivative [Ru(IEt2Me2)(PPh3)2(C6F5)H] (4) was isolated. A more efficient route to 2 involved treatment of 1 with 0.33 eq. of TREAT-HF (Et3N·3HF); excess reagent gave instead the [H2F3]- salt (5) of the known cation [Ru(IEt2Me2)2(PPh3)2H]+. Under catalytic conditions, 1 proved to be an active precursor for hydrodefluorination, converting C6F6 to a mixture of tri, di and monofluorobenzenes (TON = 37) at 363 K with 10 mol% 1 and Et3SiH as the reductant.
- Cybulski, Mateusz K.,Riddlestone, Ian M.,Mahon, Mary F.,Woodman, Timothy J.,Whittlesey, Michael K.
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- The first example of the ortho-directing effect of the weakly coordinating substituent [-BF3]- in the catalytic hydrodefluorination of the pentafluorophenyltrifluoroborate anion
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The pentafluorophenyltrifluoroborate anion undergoes hydrodefluorination under the action of zinc in the presence of nickel complexes turning into the 2,3,4,5-tetrafluoroborate anion.
- Adonin, Nicolay Yu.,Prikhod'ko, Sergey A.,Bardin, Vadim V.,Parmon, Valentin N.
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Read Online
- Rhodium catalyzed, carbon-hydrogen bond directed hydrodefluorination of fluoroarenes
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[CpRhCl(μ-Cl)]2 is reported as a highly efficient and selective precatalyst for the hydrodefluorination of perfluoroarenes using a hydrocarbon-soluble aluminum dihydride as the terminal reductant. Reactions are directed to cleave a C-F bond adjacent to an existing C-H bond with high regioselectivity (98.5-99%). A heterobimetallic complex containing an extremely rare Al-H-Rh functional group has been isolated and shown to be catalytically competent.
- Ekkert, Olga,Strudley, Sebastian D. A.,Rozenfeld, Alisa,White, Andrew J. P.,Crimmin, Mark R.
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Read Online
- Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion
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Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C6HnF(5-n)B(OH)2 with half-lives spanning 9 orders of magnitude: a and Sδ values, kinetic isotope effects (2H, 10B, 13C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra-and pentafluorophenylboronic acids but has a similar pKa.
- Cox, Paul A.,Reid, Marc,Leach, Andrew G.,Campbell, Andrew D.,King, Edward J.,Lloyd-Jones, Guy C.
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supporting information
p. 13156 - 13165
(2017/09/26)
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- Catalytic Hydrodefluorination of Fluoroarenes Using Ru(IMe4)2L2H2 (IMe4 = 1,3,4,5-Tetramethylimidazol-2-ylidene; L2 = (PPh3)2, dppe, dppp, dppm) Complexes
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The all-trans isomer of Ru(IMe4)2(PPh3)2H2 (ttt-4; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) reacts with C6F6 at 70 °C to afford the hydride fluoride complex Ru(IMe4)2(PPh3)2HF (ttt-6). At room temperature, ttt-6 reacts with Et3SiH to give a mixture of products, one of which is assigned as the silyl trihydride complex Ru(IMe4)2(PPh3)(SiEt3)H3 (8) by comparison to the isolated and structurally characterized analogue Ru(IMe4)2(PPh3)(SiPh3)H3 (9). As ttt-4 was re-formed cleanly upon heating ttt-6 with Et3SiH, it was tested in the catalytic hydrodefluorination (HDF) of C6F6 (10 mol %, 90 °C), along with 9, Ru(IMe4)2(P-P)HF (P-P = Ph2P(CH2)2PPh2 (dppe, cct-13), Ph2P(CH2)3PPh2 (dppp, cct-14), Ph2PCH2PPh2 (dppm, cct-15)), Ru(IEt2Me2)2(PPh3)2HF (cct-7; IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)), and Ru(IEt2Me2)2(dppe)2HF (cct-16) for comparison. Both cct-13 and cct-14 brought about near-quantitative conversion to C6FH5 in 24 h, in comparison to ca. 50% conversion with ttt-4 in 144 h.
- Cybulski, Mateusz K.,Nicholls, Jessica E.,Lowe, John P.,Mahon, Mary F.,Whittlesey, Michael K.
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p. 2308 - 2316
(2017/06/30)
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- Base-promoted silver-catalyzed protodeboronation of arylboronic acids and esters
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The silver-catalyzed protodeboronation of arylboronic acids and esters in the presence of a base was developed. This method was highly efficient for the protodeboronation of various arylboronic acids and was applied to an efficient deprotection of bifunctional amine under mild conditions. A base-promoted mechanism was proposed. This journal is
- Liu, Chun,Li, Xinmin,Wu, Yonghua
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p. 15354 - 15358
(2015/02/19)
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- The ionic liquid [bmim]Br as an alternative medium for the catalytic cleavage of aromatic C-F and C-Cl bonds
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The potential of [bmim]Br as an alternative to aprotic dipolar solvents in nickel-catalyzed hydrodehalogenation reactions is demonstrated. Hydrodechlorination of pentafluorochlorobenzene proceeds under the action of zinc in aqueous [bmim]Br. Under the above conditions aromatic C-F bonds also undergo slow cleavage. The reaction is significantly accelerated in the presence of nickel complexes with 2,2′-bipyridine or 1,10-phenanthroline. In the case of pentafluoroacetanilide highly regioselective ortho-hydrodefluorination leading to the formation of 3,4,5-trifluoroacetanilide is observed.
- Prikhod'ko, Sergey A.,Adonin, Nicolay Yu.,Parmon, Valentin N.
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scheme or table
p. 2265 - 2268
(2010/05/18)
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- Process for the Synthesis of Highly Active Binary Metal Fluoride as a Fluorinating Agent for Aromatics
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The subject invention relates to a process for the synthesis of highly active binary metal fluoride system for the fluorination of aromatic compounds. Fluorinated aromatic compounds are valuable synthons for the chemical synthesis of pharmaceutical drugs and novel polymers. Fluorobenzene is used to control carbon content in steel manufacturing, is an intermediate for pharmaceuticals, pesticides and other organic compounds. Fluorobenzene is typically produced by the reaction of aniline and sodium nitrite in the presence of hydrogen fluoride. The present invention relates to a process for the synthesis of highly active binary metal fluoride system consists of copper (II) fluoride and aluminum (III) fluoride for the fluorination of aromatic compounds in gas phase and recycling of the reagent, in situ, using O2 and HF.
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Page/Page column 5
(2010/02/17)
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- Method for separating substances
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An objective of the present invention is to provide electrophoretic separation methods and devices that enable the various features of a substrate surface that comes in contact with an electrophoresis medium to be controlled. The present invention provides methods for electrophoresing substances, which comprises the steps of: (a) adding a substance to be analyzed to an electrophoresis medium retained in a substrate, whose surface that has come in contact with the electrophoresis medium has been coated with a polymer membrane; and (b) adding electrophoretic pressure to the electrophoresis medium. For example, the use of a plasma-polymerized membrane allows the formation of a membrane with homogeneous quality and thickness on the surface of an arbitrary shape. In addition, desired characteristics can be conferred on the surface through selection of monomeric substances. Protein adsorption onto micro-chips can be effectively prevented as well.
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- METHOD FOR THE PRODUCTION OF 1,3,5-TRIFLUORO-2,4,6-TRICHLOROBENZENE FROM FLUOROBENZENE DERIVATIVES
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Method for the production of 1,3,5-trifluoro-2,4,6-trichlorobenzene from fluorobenzene, comprising steps A) and B): A) chlorination of fluorobenzene derivatives of formula (II), in which X = fluorine or H, Z = nitro, bromo or chloro and n = 0 or 1-4 and B) fluorination of the distillation residue and separation by distillation of the 1,3,5-trifluoro-2,4,6-trichlorobenzene thus produced.
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(2008/06/13)
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- Polyfluoroorganoboron-oxygen compounds. 2 [1]: Base-catalysed hydrodeboration of polyfluorophenyl(dihydroxy)boranes
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Polyfluorinated phenyl(dihydroxy)boranes C6H5-nFnB(OH)2 (n = 3 - 5) underwent hydrodeboration (formal replacement of the (dihydroxy)boryl group by hydrogen) in the presence of bases (MeOH, 33% H2O-MeO
- Frohn,Adonin,Bardin,Starichenko
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p. 2834 - 2838
(2008/10/08)
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- Preparation process of fluorine substituted aromatic compound
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A preparation process of a fluorine substituted aromatic compound comprising reacting an alkali metal or alkali earth metal salt of an aromatic compound having a hydroxy group with an organic fluorinating agent is disclosed. As a representative fluorinating agent, a bis-dialkylamino-difluoromethane compound, for example, 2,2′-difluoro-1,3-dimethylimidazolidine, is exemplified. According to the process, an industrially useful fluorinated aromatic compound, for example, a fluorobenzene, a fluorine substituted benzophenone, a fluorine substituted diarylsulfone can be prepared with ease in economy without specific equipment.
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- Combined experimental and theoretical study of the protonation of polyfluorobenzenes [C6H(6-n)F(n)] (n = 0-6)
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In a recent high-pressure mass spectrometric revision to the gas-phase basicity scale (J. E. Szulejko and T. B. McMahon, J. Am. Chem. Sec. 115, 7839 (1993)), it was observed that the proton affinity for hexafluorobenzene was 24 kcal mol-1 (1 kcal = 4.184 kJ) lower than the accepted National Institute of Science and Technology (NIST) database value of 177.7 kcal mol-1 (S. G. Lias et al., J. Phys. Chem. Ref. Data 17, Suppl. 1 (1988)). Furthermore, the proton affinities for most other polyfluorobenzenes were also found to differ substantially from the NIST values. For many of the polyfluorobenzenes large protonation entropy changes were noted, which were substantially greater than then those expected from rotational symmetry number changes alone. In view of these observations, MP2/6-31G**/HF/6-31G** ab initio calculations were undertaken to investigate further the proton affinity and entropy changes with respect to the degree of fluorine substitution. The present proton affinity variations found for the polyfluorobenzenes (hexaflorobenzene excepted) can be interpreted with the aid of the ab initio results in terms of a simple additivity scheme. Each fluorine substituent para, meta, ortho or ipso to the ring protonation site will induce an incremental proton affinity change with respect to benzene of 1.5, -7.0, -1.5 and -19.0 kcal mol-1, respectively. This additivity scheme can also be used to rationalize the re-evaluated proton affinities for the polymethylbenzenes and m- and o-fluorotoluenes. The corresponding methyl increments are 7.5, 5.5, 2.5 and 1.0 kcal mol-l for para, meta, ortho and ipso protonation respectively. From the present ab initio statistical thermodynamic analysis of the various protonation entropy components, it was concluded that the low frequency vibrations are almost exclusively responsible for the large excess entropy changes observed experimentally. Ab initio calculated barriers for 1,2 proton shifts in arenium species available in the literature are concluded to be too large to allow the existence of a so-called dynamic proton. Large excess protonation entropies are noted from the literature for polymethylbenzenes, naphthalene and 1-methylnaphthalene.
- Szulejko,Hrusak,McMahon
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p. 494 - 506
(2007/10/03)
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- Process for the preparation of aromatic fluoro compounds
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The invention relates to a process for the preparation of aromatic fluoro compounds of the formula I in which Ar is phenyl, naphthyl or pyridyl, R1, R2 and R3 independently of one another are hydrogen, halide, (C1 -C4)-alkyl, phenyl, NR2, OR, CN, COH or COR, where R is hydrogen or (C1 -C6)-alkyl, and n=1, 2, 3, 4 or 5, which comprises reacting aromatic fluoro compounds of the formula II in which Ar, R1, R2, R3 and n have the abovementioned meaning, each X is a chlorine or bromine atom and m=1, 2, 3, 4 or 5, with hydrogen in the presence of a palladium catalyst, a water-insoluble amine which also does not form water-soluble hydrohalides, and if desired an inert solvent.
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- Radical Anions of Aromatic Compounds. XXIV. Electrochemical Reduction of Polyhalogenated Nitrobenzene Derivatives
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Dependence of the peak potentials for reduction of complete series of fluorinated and chlorinated nitrobenzenes into radical anions on the number and position of halogen atoms has been studied by cyclic voltammetry.This dependence is described by linear relations involving standard ?p and ?m constants and also the constants that reflect the specific effect of a single ortho halogen atom and the nonadditivity of the effect of two ortho-located halogen atoms: ?o(F) 0.209, ?o,o(2F) 0.152, ?o(Cl) 0.15, and ?o,o(2Cl) 0.
- Selivanova, G. A.,Starichenko, V. F.,Shteingarts, V. D.
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p. 200 - 206
(2007/10/02)
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- THE THERMAL CYCLOADDITION OF PERFLUORO-1,3-BUTADIENE WITH BUTA-1,3-DIENE
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The major products from the cross-dimerization of butadiene and perfluorobutadiene are a 2+2-cycloadduct and a 2+4-cycloadduct.Perfluorobutadiene is the diene and butadiene is the dienophile.Minor products include the 4+4-cycloadduct, a criss-cross product, and several others containing fluorine on four membered rings.Pyrolysis converts both the 2+2- and the 2+4-adducts to the criss-cross product.Pyrolysis of the 2+2-adduct in the presence of carbon also gives 1,2,3- and 1,2,4-trifluorobenzenes.The fluorine nmr data for C4F6 cycloadducts helps assigning the structures.
- Weigert, Frank J.
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p. 125 - 131
(2007/10/02)
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- AROMATIC FLUORINE CHEMISTRY. PART 5. PREPARATION OF 2,6-DIFLUOROANILINE AND 1,2-DIFLUOROBENZENE
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The preparation of 2,6-difluoroaniline and 1,2-difluorobenzene from 1,2,3-trichlorobenzene is described.An isomeric mixture of 1-chloro-2,3-difluorobenzene and 2-chloro-1,3-difluorobenzene is obtained from KF exchange on 1,2,3-trichlorobenzene.Selective dechlorination of 1-chloro-2,3-difluorobenzene with H2 and Pd/C catalyst gives 1,2-difluorobenzene. 2,6-difluoroaniline is obtained via ammonolysis of 2-chloro-1,3-difluorobenzene.
- Pews, R. Garth,Gall, James A.
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p. 379 - 386
(2007/10/02)
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- The Gas-phase Thermal Isomerization of Some Tri- and Tetra-fluoro-Dewar Benzenes
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The kinetics of the gas-phase thermal isomerization of 1,2,3,5- and 1,2,4,5-tetrafluorobicyclohexa-2,5-diene into the corresponding tetrafluorobenzenes have been studied over a temperature range of 320-390 K and a pressure range of 100-2000 Nm-2.The reactions are homogeneous, obey a first-order law, and are unimolecular.The temperature dependence of the rate constants is given by the Arrhenius equations (1) for 1,2,3,5-tetrafluorobicyclohexa-2,5-diene, and (2) for 1,2,4,5-tetrafluorobicyclohexa-2,5-diene.The rate constants of the thermal isomerisation of 1,3,5-, 1,2,5-, and 2,3,5-trifluorobicyclohexa-2,5-diene into corresponding trifluorobenzenes have been measured at 353 K, and the following values of -log (k/s-1) were obtained: 2.3 +/- 0.2, 2.4 +/- 0.2, and 2.6 +/- 0.2, respectively.The influence of fluorine substitution on the thermal stability of the Dewar structure is discussed.
- Sztuba, Barbara,Ratajczak, Emil
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p. 823 - 826
(2007/10/02)
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